The present invention relates to a process for preparing ketones by contacting an olefin with steam in the presence of a catalyst of tin oxide and molybdenum oxide on a thermostable carrier. The present invention also relates to the catalyst used in the process.
Commonly assigned U.S. patent application Ser. No. 88,467 discloses a process for producing, e.g., acetone and methylethyl ketone by contacting a mixture of propylene or butylene, respectively, with a supported catalyst of tin oxide and molybdenum oxide. Good reaction selectivity is obtained in the process of this copending application if the mixture of olefin and steam is contacted with the catalyst and thereafter the catalyst is treated for a short time with an oxygen-rich gas mixture. An oxygen-rich gas mixture is a gas mixture having at least sufficient oxygen content so that when the mixture contacts the catalyst, the oxygen content of the catalyst becomes higher. However, the reaction mixture produced by this copending application always contains, in addition to the desired saturated ketone corresponding to the initial olefin, various by-products, such as carbon monoxide, carbon dioxide, lower acids, unsaturated hydrocarbons formed through disproportionment, and oxidation products thereof, as well as oligomers of the initial olefin. The oligomers are considered particularly undesired by-products, since they partly deposit upon the catalyst, causing the catalyst activity to decrease over the course of the reaction, thereby resulting in decreased conversion. Furthermore, by-products having a boiling point approaching that of the desired ketone product are also troublesome, since these by-products interfer with the recovery of the desired ketone from the reaction mixture.